The present invention generally relates to high speed cable or wire stranders, and more specifically to a high speed rigid-type strander in which the axes of the bobbins are oriented at substantial angles from the axis of rotation of the hollow body or main shaft to which the bobbin supporting members are rigidly connected.
When manufacturing a cable from a plurality of wires, a core wire formed by either a single wire or a plurality of already stranded wires is usually passed through the machine and other wires are wrapped around the core wire either while the core wires move along its path or at the end of the machine. This function is usually carried out by high speed machines which, as a rule, include one or more rotatable frames or housings and a plurality of wire-carrying bobbins located within the frame or carried by supports mounted on the frames.
The core wire is usually paid-off from a bobbin mounted outside the frame and passed through the frame through a path either along the axis of rotation of the frame or displaced from the axis of rotation of the frame. The way the core wire is handled characterizes the type of wire strander and its application.
If the core wire is passed through the machine along its axis of rotation, the wire carrying bobbins rotate around it and the wires paid-off are wound on the core wire at several points along the machine. This system allows the manufacture of conductors with a high number of wires and a change in direction of the various layers since the machine is composed of many sections independent of each other. Furthermore, since the core wire passes substantially along the axis of the machine, a large multi-stranded core can be used.
If the core wire is passed through the machine along a path significantly displaced from the axis of rotation of the frame, the wire carrying bobbins are positioned inside the frame along its axis of rotation and they remain stationary while the frame rotates. The cable wires are paid-off from the bobbins and the wires pass through a path displaced from the axis of rotation of the machine and are wound around the core wire at the end of the machine. This method allows the manufacture of conductors with a relatively low number of wires and the various layers of the stranded conductors must be wound in the same direction.
In the manufacturing of stranded cable from a plurality of wires, three basic types of stranders are presently used in the industry. In one type, the tubular strander, the bobbins are placed in cradles which are mounted on bearings in a tubular rotatable frame or housing. During the operation, the frame rotates while the cradles and the bobbins are stationary. The wires are paid-out or pulled from the bobbins and are brought along the frame through guides until they are wound on the core wire which is usually taken from a bobbin mounted outside the frame and passed through the frame along a path that is parallel to the axis of the machine, but significantly displaced from the center as are the other wires paid-out from the bobbins loaded on the cradles inside the tubular frame. Such a strander is shown and described in the products catalog published by Ceeco Machinery Manufacturing Limited of Concord, Ontario, Canada.
The second basic type of strander is known as a rigid strander. In this type of strander, the bobbins are usually mounted on a rigid rotatable frame and they are solidly connected to the frame itself, this machine is usually made in sections and follows the classic stranding formations of conductors made with wires of the same diameters. In the basic formation, each layer above the core wire has six more wires than the previous one. Thus, the first layer directly on the core wire has six wires, the second wire layer has twelve wires, the fourth wire layer has eighteen wires, the fifth wire layer has twenty-four wires, etc. While rigid stranders are generally slower than tubular stranders, they are more compact and are normally used to manufacture conductors of nineteen or more wires, especially in the non-ferrous industry. For conductors with a lower number of wires, tubular stranders are adopted as a rule, in view of their higher speeds. Rigid stranders are also shown and described in the above-identified Ceeco Machinery Manufacturing Limited catalog.
The third type of strander commonly used is called a planetary strander and, in many respects, is similar to the rigid strander. However, in the planetary strander the bobbins are mounted on cradles which are kept in a fixed plane through mechanical means while the machine rotates. The object of such stranding operation is to avoid any twisting of the wire during the stranding operation as is done when using a rigid frame strander. Planetary stranders are also shown and described in the above Ceeco catalog. Tubular stranders and planetary stranders do not twist the base wire during the operation and, therefore, can be used both in the ferrous and non-ferrous industries. Rigid frame stranders are used as a rule only when the base wire can be subject to twisting.
In the past, wire carrying bobbins mounted on the frame of the strander have usually been mounted so that the bobbins were required to rotate along their longitudinal axis in order to pay-off the wire. This arrangement usually requires some control of the rotation of the bobbins, such as a brake mechanism for each bobbin to provide the required wire tension and to assure that the bobbins will not continue to rotate when the frame of the strander has stopped its rotation.
The braking device causes the tension of the wire paid-off from the bobbins to vary during the operation of the strander since the wire pulling tension required to make the bobbin rotate is different when the bobbin is full or near empty. If the initial braking force is adjusted for a full bobbin, the same braking force applied to a bobbin with partially depleted wire supply is sometimes sufficient to cause unacceptable stretch, especially for wires of the smaller gauge. In such a case, the cable produced will be malformed. Also, since the braking force is applied to each bobbin before the initial start of the strander, there is a tendency to stretch the wire before the strander reaches its normal operational speed. Because of frequent malfunction of the brakes, the wires from the bobbins within the frame of the strander occasionally continue to pay-out after the strander has been stopped, and because different brake forces are applied to different bobbins, different tensions are created in the wire paid-out from the bobbins. Therefore, many times the cable formed by traditional stranders have one or more wires loosely wrapped with the remaining wire more tightly wrapped.
One attempt to overcome some of the above-mentioned problems was to fly-off the wires from stationary bobbins since this provided a better means of controlling the tension irrespective of the amount of wire remaining on the bobbin. A fly-off system introduced for stranders having a core wire path significantly displaced from the axis of rotation of the machine and the wire carrying bobbins positioned within the tubular frame with longitudinal axes both parallel and perpendicular to the axis of rotation of the frame. For example, in U.S. Pat. No. 3,827,225, for "High Speed Strander", both a tubular and a rigid strander are disclosed wherein the wires fly off bobbins which are mounted on shafts parallel to the axis of the machine rotating frame. With respect to the tubular strander disclosed in the above patent, the bobbins are positioned along the axis of rotation of the tubular, cylindrical frame and, therefore, the core wire cannot pass through the axis of rotation, but is displaced therefrom as in conventional tubular stranders. This presents a disadvantage inasmuch as it limits the size of the core wire which may be used. With respect to the rigid strander disclosed in the above patent, wherein the core wire passes along the axis of rotation of the frame and where the bobbins are mounted on the frame with their longitudinal axes approximately parallel to the axis of the machine, the rigid strander disclosed has several disadvantages because, while the wire flies off during rotation of the frame, it is subject to significant variations in centrifugal forces which tend to push the wire outwardly, thus creating oscillations of the wire tension. This is particularly severe when using large bobbins as is the case in the industry, since such tension variations may result in fluctuations in tightness of the finished stranded product. Another disadvantage of the rigid-type strander disclosed in the above patent is that the bobbins must be mounted on cantilevered shafts parallel to the axis of rotation, thus limiting the size of bobbins that can be used or causing a severe reduction in the speed of the machine since large bobbins and high speeds would subject the cantilevered shaft to excessive stresses. The disclosed configuration also requires that the bobbins be positioned far from the axis of rotation, thus increasing the centrifugal forces that come into play. In order to maintain the same total number of bobbins while decreasing the radial distances at which the shafts are mounted from the axis of rotation, the overall length of the machine may have to be increased to an undesirable or impractical length.
Another fly-off, tubular-type strander is disclosed in U.S. Pat. No. 3,902,307 for "Modified High Speed Strander". This patent discloses a tubular-type strander which includes a hollow cylindrical housing or tube inside which a plurality of bobbins are supported along the axis of rotation of the cylindrical housing. With this strander, the bobbins are situated on the axis of rotation to avoid significant centrifugal forces thereon. Consequently, as with stranded tubular stranders, the core wire cannot go through the center or axis of rotation of the frame or housing, but must be bent or deflected at least four times as the core wire is guided along the axis, and thence along the housing wall, and finally moved towards the housing axis. Such displacement of the core wire from the axis of rotation, as suggested above, limits the size of the core wire which can be used and, therefore, limits the size of the overall product which can be handled or produced by the strander.
In the tubular-type strander disclosed in both of the above-identified patents, the bobbin supporting stems or shafts are pivotally connected to the cylindrical housings by means of pivot arrangements to permit the bobbins to be loaded and removed through relatively small openings in the tubular or cylindrical housings. Such constructions have made these stranders more complicated, and more inconvenient to use.